Footage of black-clad protesters apparently making a barricade

Scene tense as police move in

Police helicopters were circling overhead the tense scene on a street running alongside the Elbe river harbour with its container cranes, and near mural-covered former squats that saw heavy clashes with police in the 1980s, AFP reports.

Protesters were seen scrambling to leave the scene, some changing out of their all-black gear, as police announced that the organisers have called off the march following the clashes.

Riot police move in through the smoke during the "Welcome to Hell" rally against the G20 summit in HamburgCredit: AFP

Police 'demanded protesters remove their masks'

Police say they repeatedly asked a group of hardcore anti-capitalist demonstrators to remove their masks Thursday evening, to no avail. They then decided to separate the group from the rest of the several thousand-strong demonstration.

Black-hooded protesters attacked a police vehicle with bottles and bricks, breaking its window.

The violence broke out near the start of the demonstration at a riverside plaza used for Hamburg's weekly fish market.

German riot policeman catches a protester during the demonstrationsCredit: Reuters